Need some Xbox Live help...

I got my internet turned back on today and picked up an Xbox Live prepaid card to get back in some CoD: MW2. When I got home I entered the code into the Redeem code section instead of going into "Manage Accounts" first.
Well, now it won't let me upgrade to a Gold membership using the points I just bought.
Am I missing a certain selection somewhere in there or what? It's driving me absolutely crazy.